Lecture notes for Unit-1 "Fundamentals of DBMS" for semester Summer-2020

1. 1
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
Unit-1: Fundamentals of DBMS
* Traditional file-based approach *
 The term 'file-based approach' refers to the situation where data is stored in
one or more separate computer files defined and managed by different
application programs.
 Typically, for example, the details of customers may be stored in one file,
orders in another, etc.
 Computer programs access the stored files to perform the various tasks
required by the business.
 Each program, or sometimes a related set of programs, is called a computer
application.
 For example, all of the programs associated with processing customers' orders
are referred to as the order processing application.
 The file-based approach might have application programs that deal with
purchase orders, invoices, sales and marketing, suppliers, customers,
employees, and so on.
 The following diagram shows how different applications will each have their
own copy of the files they need in order to carry out the activities for which
they are responsible:
2
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
 One approach to solving the problem of each application having its own set of
files is to share files between different applications.
 The introduction of shared files solves the problem of duplication and
inconsistent data across different versions of the same file held by different
departments, but other problems may emerge, including:
o Physical data dependence:
 If the structure of the data file needs to be changed in some
way (for example, to reflect a change in currency), this

2. 3
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
alteration will need to be reflected in all application programs
that use that data file.
 This problem is known as physical data dependence, and will
be examined in more detail later in the chapter.
o Difficult to implement concurrency:
 While a data file is being processed by one application, the
file will not be available for other applications or for ad hoc
queries.
 This is because, if more than one application is allowed to
alter data in a file at one time, serious problems can arise in
ensuring that the updates made by each application do not
clash with one another.
 This issue of ensuring consistent, concurrent updating of
information is an extremely important one, and is dealt with
in detail for database systems in the chapter on concurrency
control.
 File-based systems avoid these problems by not allowing
more than one application to access a file at one time.
The database approach
 The database approach is an improvement on the shared file solution as the
use of a database management system (DBMS) provides facilities for
querying, data security and integrity, and allows simultaneous access to data
by a number of different users.
4
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
DBMS File System
DBMS is a collection of data.
In DBMS, the user is not
required to write the
procedures.
File system is a collection of data. In this
system, the user has to write the procedures
for managing the database.
DBMS gives an abstract view
of data that hides the details.
File system provides the detail of the data
representation and storage of data.
DBMS provides a crash
recovery mechanism, i.e.,
DBMS protects the user from
the system failure.
File system doesn't have a crash
mechanism, i.e., if the system crashes while
entering some data, then the content of the
file will lost.
DBMS provides a good
protection mechanism.
It is very difficult to protect a file under the
file system.
DBMS contains a wide variety
of sophisticated techniques to
store and retrieve the data.
File system can't efficiently store and
retrieve the data.
DBMS takes care of
Concurrent access of data using
some form of locking.
In the File system, concurrent access has
many problems like redirecting the file
while other deleting some information or
updating some information.

3. 5
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
* The database approach *
 The database approach is an improvement on the shared file solution as the
use of a database management system (DBMS) provides facilities for
querying, data security and integrity, and allows simultaneous access to data
by a number of different users.
 One of the benefits of the database approach is that the problem of physical
data dependence is resolved, this means that the underlying structure of a data
file can be changed without the application programs needing amendment.
 This is achieved by a hierarchy of levels of data specification. Each such
specification of data in a database system is called a schema.
 The different levels of schema provided in database systems are described
below.
6
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
 The internal schema
o The internal level has an internal schema which describes the physical
storage structure of the database.
o The internal schema is also known as a physical schema.
o It is used to define that how the data will be stored in a block.
o The physical level is used to describe complex low-level data structures in
detail.
 Conceptual Level
o The conceptual schema describes the design of a database at the conceptual
level. Conceptual level is also known as logical level.
o The conceptual schema describes the structure of the whole database.
o The conceptual level describes what data are to be stored in the database
and also describes what relationship exists among those data.
o In the conceptual level, internal details such as an implementation of the
data structure are hidden.
o Programmers and database administrators work at this level.
 External Level
o At the external level, a database contains several schemas that sometimes
called as subschema.
o The subschema is used to describe the different view of the database.
o An external schema is also known as view schema.
o Each view schema describes the database part that a particular user group
is interested and hides the remaining database from that user group.
o The view schema describes the end user interaction with database
systems.

4. 7
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
* DBMS Architecture *
 The DBMS design depends upon its architecture.
 The basic client/server architecture is used.
 DBMS architecture depends upon how users are connected to the database to
get their request done.
 Types of DBMS Architecture
Database architecture can be seen as a single tier or multi-tier. But
logically, database architecture is of TWO types like: 2-tier architecture and 3-
tier architecture.
 1-Tier Architecture
o In this architecture, the database is directly available to the user. It means
the user can directly sit on the DBMS and uses it.
o Any changes done here will directly be done on the database itself.
o The 1-Tier architecture is used for development of the local application,
where programmers can directly communicate with the database for the
quick response.
 2-Tier Architecture
o The 2-Tier architecture is same as basic client-server. In the two-tier
architecture, applications on the client end can directly communicate with
the database at the server side. For this interaction, API's like: ODBC,
JDBC are used.
o The user interfaces and application programs are run on the client-side.
o The server side is responsible to provide the functionalities like: query
processing and transaction management.
o To communicate with the DBMS, client-side application establishes a
connection with the server side.
8
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
 3-Tier Architecture
o The 3-Tier architecture contains another layer between the client and
server. In this architecture, client can't directly communicate with the
server.
o The application on the client-end interacts with an application server which
further communicates with the database system.
o End user has no idea about the existence of the database beyond the
application server. The database also has no idea about any other user
beyond the application.
o The 3-Tier architecture is used in case of large web application.

5. 9
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
* Storage Structures *
We can discuss the storage structures of DBMS under the two sub-
sequent titles:
1. Storage System
2. Storage Structures (File Structures)
1. Storage System:
o Databases are stored in file formats, which contain records.
o At physical level, the actual data is stored in electromagnetic format on
some device.
o These storage devices can be broadly categorized into three types:
a) Primary Memory
b) Secondary Memory
c) Territory Memory
2. Storage Structures:
o A file is a sequence of records stored in binary format.
o A disk drive is formatted into several blocks that can store records.
o File records are mapped onto those disk blocks.
o Storage Structures defines how file records are mapped onto disk blocks.
o We have four types of storage structures to organize file records:
10
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
A. Heap File Organization:
o When a file is created using Heap File Organization, the Operating System
allocates memory area to that file without any further accounting details.
o File records can be placed anywhere in that memory area.
o It is the responsibility of the software to manage the records.
o Heap File does not support any ordering, sequencing, or indexing on its
own.
B. Sequential File Organization:
o Every record in the file contains a data field (attribute) to uniquely identify
that record.
o In sequential file organization, records are placed in the file in some
sequential order based on the unique key field or search key.
o Practically, it is not possible to store all the records sequentially in
physical form.
C. Hash File Organization:
o Hash File Organization uses Hash function computation on some fields
of the records.
o The output of the hash function determines the location of disk block
where the records are to be placed.
D. Clustered File Organization:
o Clustered file organization is not considered good for large databases.
o In this mechanism, related records from one or more relations are kept in
the same disk block, that is, the ordering of records is not based on primary
key or search key.

6. 11
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
* Data Representation in DBMS *
 We know that data is core component of DBMS.
 DBMS is a software which provides facilities for storage and management of
data in the database.
 Data stored using DBMS systems forms a hierarchy extending from a single
bit to a database.
 Data are logically organized into:
1. Bits (8-bits: A character)
2. Fields
3. Records
4. Files
5. Databases
Bit -
o A bit is the smallest unit of data representation (value of a bit may be a 0
or 1).
o Eight bits make a byte which can represent a character or a special symbol
in a character code.
Field –
o A field consists of a grouping of characters.
o A data field represents an attribute (a characteristic or quality) of some
entity (object, person, place, or event).
Record –
o A record represents a collection of attributes that describe a real-world
entity.
o A record consists of fields, with each field describing an attribute of the
entity.
12
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
File –
o A file consists of group of related records.
o Files are frequently classified by the application for which they are
primarily used (employee file).
o A primary key in a file is the field (or fields) whose value identifies a record
among others in a data file.
Database –
o It is an integrated collection of logically related records or files.
o A database is large collection of data organized in the form of records in
separate but related files that provides data for many applications.
o The data is managed by systems software called database management
systems (DBMS).
o The data stored in a database is independent of the application programs
using it and of the types of secondary storage devices on which it is stored.

7. 13
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
* Data Dictionary *
 Data about data is called as Metadata.
 A simple example of metadata for a document might include collection of
information like the author, file size, date the document was created, etc.
 A data dictionary is a file or a set of files that contains metadata of databases.
 What data dictionary consists of:
 Name of the tables in the database
 Constraints of a table i.e. keys, relationships, etc.
 Columns of the tables that are related to each other.
 Owner of the table.
 Last accessed information of the object.
 Last updated information of the object.
Types of Data dictionary:
There are TWO types of data dictionaries in DBMS:
1. Active Data Dictionary
2. Passive Data Dictionary
1. Active Data Dictionary:
The DBMS software manages the active data dictionary automatically.
The modification is an automatic task and most RDBMS has active data
dictionaries.
It is also known as integrated data dictionary.
2. Passive Data Dictionary:
Managed by the user and is modified manually when database structure
changes.
It is also called as non-integrated data dictionary.
14
Prepared by, B.Sc. CPS (IV Sem)
Mr. Hushare Y.V. [M.Sc., MCA, SET], Assistant Professor RDBMS & PL/SQL(Unit-1)
DBA
 The DBA stands for Database Administrator.
 A DBA is treated as role in DBMS or as one type of user of DBMS.
 The DBA requires technical training and expertise in the specific DBMS that
organization is using.
 Following are the responsibilities of DBA:
 Installation, configuration and upgradation of DBMS software.
 Evaluating the features of various DBMS.
 Establishing and maintaining sound backup and recovery policies an
procedures.
 Taking care of database design and implementation.
 Implementing and maintaining the database security.
 Maintaining documentation and standards.
 DBA does some technical troubleshooting and consultation to
development teams.
Types of DBA:
 There are different types of DBA’s depending upon the organization’s
requirements:
1. Administrative DBA:
 Administrative DBA maintains the work on the server and keeps it
running.
 Administrative DBA is mostly concerned with backups, security, etc.
2. Development DBA:
 Development DBA builds queries, stored procedures etc. which mostly
meet business needs.
 Development DBA is equivalent to a programmer but with some more
privileges.
3. Data Architect DBA:
 This DBA builds table, design schema, foreign keys, primary keys, etc.
which meets business needs.
4. Data Warehouse DBS:
 Data warehouse DBA is responsible for merging the data from multiple
sources into a data warehouse.